1. Field of the Invention
The present invention relates in general to a control system for a power steering device and particularly, to such a control system for controlling the supply and exhaust of pressurized fluid to and from a power cylinder of the power steering device in accordance with various control inputs such as vehicle speed, steering angle, manual steering torque and so forth.
2. Description of the Prior Art
In power steering devices, generally, a servovalve is actuated upon receipt of steering torque manually applied to a steering wheel mechanically coupled thereto so that the supply and exhaust of pressurized fluid to and from a power cylinder is controlled. For the purpose of controlling its steering characteristic in response to various parameters such as steering angle, vehicle speed and so forth, a known power steering device of this type is provided with a solenoid valve in addition to the above-noted servovalve. This solenoid valve controls the pressure of fluid supplied to a counterforce generating chamber of the servovalve or controls the flow volume of fluid bypassed from a supply passage directly to an exhaust passage without passing through the servovalve.
As noted above, the prior control system requires the solenoid valve or the like for steering characteristic control, in addition to the mechanically actuated servovalve. This disadvantageously results in an expensive control system, and one which is liable to be limited only to the controlling of steering force.